New Design Mixer Solution for Millimeter-Wave Spectrum Analysis

More and more services are using wideband millimeter-wave wireless communications, such as wireless backhaul in the 60 GHz to 80 GHz band, WiGig WLAN modules (IEEE 802.11ad) in the 60 GHz band, and automotive radar in the 77 GHz and 79 GHz bands.
Conventional millimeter-wave measurements use a harmonic mixer or down converter but there are various problems when using these setups to measure wideband signals. The High Performance Waveguide Mixer MA2806A and MA2808A are the new solutions for these problems.

*1: High noise floor level and narrow dynamic range due to high mixer conversion order
*2: Low IF frequency depending on spectrum analyzer causes occurrence of image response generated in measurement range
*3: Narrow dynamic range due to mixer P1dB performance of only -10 to -5 dBm
*4: Different calibration procedure depending on spectrum analyzer used
*5: Requires mixer conversion loss data for measurement range because any IF frequency can be set

In case of 77/79 GHz automotive radar, the phase noise performance is important to detect the objects at short distance and person moving slowly.
The High Performance Waveguide Mixer MA2806A/MA2808A support excellent phase noise performance in combination with the Signal Analyzer MS2840A. For example, the phase noise performance is better than –100 dBc/Hz in the 79 GHz frequency band with an offset of either 10 kHz or 100 kHz.
Additionally,Phase Noise Measurement Opt-010 simplifies procedures and improves test time.

Five Key Features of Anritsu High Performance Waveguide Mixers

Does Your Current System Support Millimeter-Wave Spectrum Analysis?

Until now, evaluating the Tx characteristics of millimeter-wave wireless equipment required the combined use of a spectrum analyzer and harmonic mixer, causing two problems resulting from widening channel bandwidths:

Anritsu's New Millimeter-Wave Solution Solves These Problems

Problem 1: Poor Minimum Sensitivity Performance
For example, accurate Over-The-Air (OTA) measurements of IEEE 802.11ad WLAN (WiGig) modules require use of instruments with excellent minimum sensitivity performance, because the level of the signal input to the instrument is very small as a result of the large free-space propagation loss.
Additionally, at RF Spectrum Mask tests*1 of wireless backhaul Out Door Units (ODU) using a connected waveguide, the large connection loss of the harmonic mixer makes it impossible to ensure sufficient measurement margin matching the measurement standards. As future channel bandwidths widen to 1 GHz to 2 GHz, minimum sensitivity will be a key issue affecting inability to secure the necessary measurement margin.*1: ETSI EN 302 217-2-2 4.2.4 RF Spectrum Mask

Solution 1: Use High Performance Waveguide Mixer MA2806A/MA2808A to Achieve Excellent Minimum Sensitivity Performance
By using a dedicated multiplier, low-noise amplifier (LNA), bandpass filters (BPF), etc., the MA2806A and MA2808A have an excellent conversion loss of at least 10 dB better than conventional harmonic mixers. When used in combination with the Spectrum Analyzer/Signal Analyzer MS2840A/MS2830A, the display average noise performance level is excellent at -150 dBm/Hz (meas)*2 at 75 GHz. Due to this excellent minimum sensitivity performance, it has plenty of margin for evaluating increasingly wider-band millimeter-wave equipment.*2: Value measured at design but not guaranteed specification.

Problem 2: Occurrence of Image Responses in Measurement Range
Measurements using a mixer sometimes suffer from the appearance of signals at about the same level but at different frequencies from the actual input signal. When down-converting a millimeter-wave signals, the true signal and non-existent signals (called image responses) are down-converted at the two locations where the oscillator local frequency is ‘actual input signal – IF frequency’ and ‘actual input signal + IF frequency,’ causing image responses at frequencies of twice the IF frequency from the input signal.
Image response can be eliminated by inserting a preselector in front of the mixer. However, although measurement is possible across the entire frequency range without any effect of image response due to the preselector, the Rx sensitivity performance is degraded badly by the large preselector insertion loss.
Generally, measurements that do not display image responses are either wideband spurious measurements or spectrum mask measurements measuring close to the target signal. For spurious measurements, the measured span is divided into parts and an image response is avoided by measuring so that each span does not exceed the IF frequency × 2.
For spectrum mask measurements, the input signal is positioned at the center frequency of the measurement screen and the range that can be measured without image-response effects becomes ±(IF frequency × 2 – Bn*3/2) MHz.
For example, for an RF Spectrum Mask test for 2-GHz bandwidth wireless backhaul using a spectrum analyzer and a harmonic mixer IF frequency of 400 MHz, since an image response is displayed at a frequency of ±0.8 GHz from the input signal, the spectrum cannot be measured because the image response is displayed superimposed on the target signal with 2-GHz bandwidth.*3: Input signal bandwidth [MHz]

Solution 2: Use High IF Frequency for Wider Measurement Span
Anritsu understands the importance of Rx sensitivity performance and has developed a method to reduce the problems of measuring image response as far as possible, without using a preselector. The measurable span without image-response effects is two times the IF frequency. Since it operates at a high IF frequency of 1.875 GHz, combining the MS2840A/MS2830A with the MA2806A/MA2808A supports an image-response-free range of 3.75 GHz (2 x 1.875 GHz). At Spectrum Mask tests, the range is 3.75 GHz – Bn/2, where Bn is the signal bandwidth. For example, when Bn is 1 GHz at a wireless backhaul RF Spectrum Mask test, the 4 GHz measurement span standardized by ETSI to prevent the appearance of an image response at 6.5 GHz is unaffected by an image response. However, when Bn is either 2 GHz at the standardized 7 GHz measurement span, or 1.88 GHz at the standardized 6.12 GHz measurement span for the WiGig (802.11ad) Transmit Mask test*4, the span described by the above equation that can be measured with no image-response effect, is either 5.5 GHz or 5.62 GHz, respectively, which does not satisfy the standard. Using the newly developed PS function*5 supports measurements up to a span of 7.5 GHz (3.75 GHz × 2) without image-response effects.*4: IEEE Std 802.11ad-2012 21.3.2 Transmit mask*5: Patent pending as of October 2015

Problems When Substituting a Down Converter for Harmonic Mixer

One method for solving harmonic mixer problems is using a down converter instead.
A down converter is a customer-configured measurement system using a mixer, signal generator for the LO signal, and multiplier. The conversion loss is small due to the primary mixing and conversion to a high IF frequency easily suppresses image response effects.
However, down converters have the following three problems:

Anritsu’s New Millimeter-Wave Solution Solves These Problems Too

Problem 3: Poor Minimum Sensitivity Performance due to Low P1dB*6Performance
As well as minimizing mixer conversion loss, P1dB performance is a key point in assuring excellent minimum sensitivity performance. P1dB is the input level when the conversion gain is compressed by 1 dB than the normal linear gain. For accurate measurement, something like an external attenuator is inserted to adjust the level so this input level is not exceeded, but this degrades the noise floor of the measurement system in proportion to the attenuation amount. Accordingly, a mixer with excellent P1dB performance can suppress this noise floor degradation. The P1dB performance of most commonly available down converters is on the order of -10 to -5 dBm, which is insufficient for measuring wideband signals.*6: Input level at 1 dB gain compression

Solution 3: High Performance Waveguide Mixer with Excellent P1dB Performance
The MA2806A and MA2808A have a superior P1dB performance exceeding 0 dBm. Since this enables a 5 to 10 dB reduction in the external attenuator value compared to conventional down converters, it prevents degraded measurement system minimum sensitivity.

Problem 4: Complex Equipment Configuration
Using a down converter requires connecting the mixer, LO signal generator and multiplier with coaxial cables, as well as correct operation of each piece of equipment, requiring quite a lot of set-up time before starting tests. Moreover, preventing spurious in the LO signal requires severe reduction of the multiplier rate, in turn necessitating an expensive microwave signal generator and high equipment costs.

Solution 4: Simple Equipment Configuration using High Performance Waveguide Mixer
Since the MA2806A and MA2808A have a built-in multiplier, the system is easily configured using a single coaxial cable connection to the MS2830A. Furthermore, no expensive microwave signal generator is required, because the MS2830A LO signal source is used.

Problem 5: More Work Calibrating Conversion Loss Data
When using a customer-configured measurement system with conventional down converter, data such as the conversion loss must be collected before measurement to calibrate the measured data. This calibration data collection is time consuming and delays the start of measurement, reducing efficiency.

Solution 5: Provided Mixer Conversion Loss Data
The MA2806A/MA2808A conversion loss data for the full frequency range is pre-saved at shipping inspection to an accessory USB memory stick. Corrected measurement results can be read directly by reading this data at the MS2830A USB port using one-touch operation.